package org.udp;

import java.io.IOException;
import java.net.BindException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
import java.nio.charset.StandardCharsets;

/**
 * 基于UDP的回显服务器
 */
public class UDPEchoServer {
    //声明一个用于提供UDP服务的对象
    private DatagramSocket socket;

    //构造方法指定服务器的端口号
    public UDPEchoServer(int port) throws SocketException {
        if (port > 65535 || port < 1024) {
            throw new BindException("端口号必须在1025~65535之间");
        }
        //初始化UDP服务端对象
        this.socket = new DatagramSocket(port);
    }

    /**
     * 处理用户请求
     */
    public void start() throws IOException {
        System.out.println("服务器已启动");
        while (true) {
            //1.使用DatagramPacket来接收用户发来的数据
            DatagramPacket requestPacket = new DatagramPacket(new byte[1024], 1024);
            //2.接收数据
            socket.receive(requestPacket);
            //3.解析接收到的数据
            String request = new String(requestPacket.getData(),
                    0, requestPacket.getLength(), "utf-8");
            //4.通过请求计算响应
            String response = process(request);
            //5.使用DatagramPacket封装响应的数据
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(StandardCharsets.UTF_8),
                    0, response.getBytes().length, requestPacket.getSocketAddress());
            //6.发送响应
            socket.send(responsePacket);
            //7.打印日志
            System.out.printf("[%s:%d] request = %s, response = %s\n",requestPacket.getAddress().toString(),requestPacket.getPort(),request, response);

        }
    }

    protected String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UDPEchoServer server = new UDPEchoServer(8888);
        server.start();
    }
}

